1. Technical Field
The present invention relates to a liquid ejecting head having serial liquid flow channels that span from a common liquid chamber formed in a flow channel formation plate to nozzle openings through pressure chambers, and to a liquid ejecting apparatus that includes such a liquid ejecting head.
2. Related Art
An ink jet recording head (called simply a “recording head” hereinafter) used in an image recording apparatus (liquid ejecting apparatus) such as a printer, a coloring material ejecting head used in the manufacture of color filters for liquid-crystal displays and the like, an electrode material ejecting head used to form electrodes for organic EL (electroluminescence) displays, FEDs (field emission displays) and the like, a bioorganic matter ejecting head used in the manufacture of biochips (biochemical devices), and so on can be given as examples of liquid ejecting heads that eject liquid droplets from nozzle openings by causing pressure fluctuations in a liquid within pressure chambers.
In the examples mentioned above, the recording head is configured so as to include a flow channel unit that has: a nozzle plate in which a plurality of nozzle openings are provided; a flow channel formation plate in which channel portions formed of spaces, grooves, and so on are provided so as to define serial ink flow channels that span from a common ink chamber to the nozzle openings through pressure chambers; and an elastic plate (also called a sealing plate, which seals the open surface of the flow channel formation plate) in which regions corresponding to the pressure chambers elastically deform based on operations of pressure generation elements (for example, see JP-A-2000-177119, and FIG. 4, FIG. 10, and so on in that document). Of the constituent elements of the flow channel unit, a high processing finesse and processing accuracy are required for the flow channel formation plate in order to handle increased resolutions in recorded images, increased speeds in recording operations, and so on. Accordingly, a silicon single-crystal substrate (a silicon wafer), in which fine shapes can be formed at a high degree of dimensional precision through anisotropic etching or the like, is favorable for use as the material of the flow channel formation plate. However, a plate member made of a metal such as stainless steel is used as the material of the nozzle plate and the elastic plate, due to the ease of processing such a material.
As described above, flow channel portions such as a through-hole (called simply a “reservoir” hereinafter) that serves as the common ink chamber are provided in the flow channel formation plate through anisotropic etching or the like; according to the recording head disclosed in JP-A-2000-177119, and FIG. 4, FIG. 10, and so on in that document, the end regions in the reservoir are formed in a tapered shape that narrows gradually as the reservoir approaches those ends. Doing so makes it possible to ensure a smooth ink flow at the end regions of the reservoir, and makes it possible to prevent bubbles from accumulating in these regions.
With the constituent elements of the flow channel unit that is configured of the stated nozzle plate, flow channel formation plate, and elastic plate, an adhesive is interposed between those constituent elements, and the constituent elements are affixed to each other by heating and curing the adhesive. However, in the case where the flow channel formation plate is configured of silicon and the nozzle plate is configured of a plate member made of a metal such as stainless steel, there are differences in the coefficients of linear expansion between those constituent elements; thus changes in temperature caused by heating and cooling during the affixing can cause the constituent elements to extend and contract relative to each other, resulting in the constituent elements deforming. At that time, because the edges of the flow channel formation plate are more rigid than the center in which the flow channel portions are provided, stress is concentrated at the border area between the high-rigidity regions and the low-rigidity regions; this can cause cracks to appear in the flow channel formation plate. In particular, in the case where the end regions of the reservoir have a tapered shape as in the example disclosed in JP-A-2000-177119, and FIG. 4, FIG. 10, and so on in that document, due to the taper, stress is concentrated in the tapered portions; as a result, it is easy for cracks to appear from the tapered ends.
If cracks appear in the flow channel portions such as the reservoir in such a manner, ink may leak to the exterior of the recording head through the cracks, or ink that has leaked through a crack may enter into the flow channel portion corresponding to another color of ink and intermix with that ink.